1. Field of the Invention
The present invention relates to an improved electric signal to pneumatic signal transducer apparatus.
2. Prior Art
Various electric signal to pneumatic signal transducers which convert an electric signal into a pneumatic signal for controlling valves and the like have been advanced. In recent years they have consisted principally of some variation of the single nozzle-flapper. In hydraulic applications, as opposed to pneumatic applications, both a fixed nozzle-fixed receiver with a plate variably interposed between them and a fixed nozzle-pair of fixed receivers with a slotted deflector have been utilized.
The single nozzle-flapper transducer is constructed with a nozzle connected to a pneumatic supply with a restriction imposed between the pneumatic supply and the nozzle. Typical of such devices are those detailed in U.S. Pat. Nos. 2,914,076 and 3,456,669. A flapper is located directly in front of the nozzle. The flapper is moved closer to or further from the nozzle responsive to an electrical input signal. The back pressure generated by the flapper between the nozzle and the restriction is the output pneumatic signal and varies as a function of the flapper's distance to the nozzle. This construction has inherent limitations, including the flapper being susceptible to erosion from grit in the gas stream and to contaminant buildup on the restriction and nozzle which eventually plugs the device. Additionally, expensive and sophisticated methods of damping the flapper to prevent it from oscillating in the gas flow due to externally applied vibration and ultimately striking the mouth of the nozzle are required.
The hydraulic transducer construction incorporates a plate inserted between a fixed nozzle and a fixed receiver to block the flow to the receiver responsive to an electric input signal. Typical of these devices are those detailed in U.S. Pat. Nos. 3,095,906 and 3,455,330. A disadvantage of this mechanization when compared to the instant invention is that it requires a plate of high mass which results in a high inertia loading for the actuator. Additionally, the plate must have a large range of motion to effect the desired results and must interact with substantially the entire hydraulic flow. This results in a transducer that has low gain while requiring high energy consumption to drive the plate.
While physically, this device appears to be close prior art that is known, since it does employ a fixed nozzle and receiver, conceptually, it is remote from the instant invention since the principle of operation is completely different. In the prior art, the hydraulic transducer varies the flow to the receiver by physically blocking the hydraulic fluid with a plate interposed between the nozzle and receiver. The instant invention relies on the aerodynamic interaction between the deflector and the gas stream to vary the flow to the receiver. Such use of aerodynamic interaction is not known in the prior art and overcomes many of the disadvantages of the hydraulic transducer.
The second hydraulic device has a fixed nozzle and a pair of fixed receivers. A slotted deflector is moved laterally with respect to the liquid stream to direct the liquid stream primarily to either of the receivers as desired. Such devices are detailed in U.S. Pat. Nos. 3,542,051 and 3,612,103. This type of device has the same disadvantages as the previously mentioned hydraulic transducer. Conceptually these devices too are remote from the instant invention. The slotted deflector interacts with the entire fluid stream. In effect, by moving the slot of the deflector, the shape of the nozzle opening is changed to redirect the direction of flow. Such means of changing flow direction are unrelated to the aerodynamic interaction of the instant invention.